For example, with regard to an information recording medium, such as an optical disc, like a CD-ROM (Compact Disc-Read Only Memory), a CD-R (Compact Disc-Recordable), and a DVD (Digital Versatile Disk)-ROM, there has been also developed an optical disc of a multilayer type or double layer type or multiple layer type in which a plurality of recording layers are laminated on the same substrate. More specifically, a dual-layer type optical disc, i.e. a two-layer type optical disc, has a first recording layer which is on the nearest side viewed from the irradiation side of laser light in recording by using an information recording apparatus (i.e. on the closest side to an optical pickup), as a first layer (wherein the first recording layer is referred to as a “L0 layer”, as occasion demands, in this application). Moreover, it has a semi-transparent reflective film located on the rear side of the first recording layer (i.e. on the farther side viewed from the irradiation side of the laser light). The dual-layer type optical disc has a second recording layer which is located on the rear side of the semi-transparent reflective film via a middle layer, such as an adhesion layer, as a second layer (wherein the second recording layer is referred to as a “L1 layer”, as occasion demands, in this application). Moreover, it has a reflective film located on the rear side of the second recording layer. Then, in preparing such a multilayer type information recording medium, the L0 layer and the L1 layer may be separately formed, and they are bonded together in the end, to thereby produce the dual-layer type optical disc at low cost.
In the information recording apparatus, such as a CD recorder, for recording information onto such a dual-layer type optical disc, the information is recorded into the L0 layer in a rewritable method or irreversible change recording method such as irreversible change recording heat by using heat or the like, by focusing the laser light for recording onto the L0 layer, and the information is recorded into the L1 layer in a rewritable method or irreversible change recording method by heat or the like, by focusing the laser light onto the L1 layer.
Patent document 1: Japanese Patent Application Laying Open NO. 2000-311346